Double-meshing-type silent chain drive and sprocket used therein

ABSTRACT

A double-meshing-type silent chain of a silent chain drive includes link plates having the identical side profile. Each link plate has two meshing teeth and a flat back face formed opposite to the meshing teeth. Two kinds of links are alternately arranged in the longitudinal direction of the chain, while the adjacent links are connected by pins. In one kind of link, an odd number of the link plates are disposed in the width direction of the chain. In the other kind of link, an even number of the link plates are disposed in the width direction of the chain. In each link, the link plates are oriented such that the meshing teeth of link plates located at widthwise opposite ends project outwardly with respect to the chain and the meshing teeth of the remaining link plates project inwardly with respect to the chain. Various types of sprockets used for meshing with the double-meshing-type silent chain are also disclosed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a double-meshing-type silentchain drive having a silent chain capable of meshing with sprocketslocated inside and outside the chain and also to a sprocket for use inthe double-meshing-type silent chain drive.

[0003] 2. Description of the Related Art

[0004] Conventionally, in some cases, a double-meshing-type silent chaincapable of meshing with sprockets or toothed pulleys which are mountedon respective driven shafts located inside and outside the chain is usedas a timing chain for transmitting rotational motion from the crankshaftof an engine to the cam-shaft of the engine or to the shaft of anauxiliary device such as an oil pump. A double-meshing-type silent chainis employed when driven shafts located inside and outside the chain mustbe rotated in opposite directions.

[0005]FIG. 17 shows a conventional double-meshing-type silent chain. InFIG. 17, an endless chain A1 meshes with a sprocket A2 located insidethe chain A1 as well as with a toothed pulley A3 located outside thechain A1.

[0006] In the chain A1, links, each composed of three kinds of linkplates having different shapes, are connected by pins A4. Specifically,guide link plates A5 are disposed at the widthwise outermost sides ofthe chain A1 as well as alternately along the longitudinal direction ofthe chain A1. As shown in FIG. 18, the guide link plate A5 has astraight edge portion a formed at the inner circumferential side of thechain A1 and two small meshing teeth b which are formed at the outercircumferential side of the chain A1 to be located at longitudinallyopposite end portions of the guide link plate 5. The small meshing teethb mesh with the toothed pulley A3.

[0007] A link plate A6 is pin-connected with adjacent guide link platesA5 at opposite end portions thereof such that the link plate A6 is incontact with inside faces of the guide link plates A5. The link plate A6has two meshing teeth c formed at the inner circumferential side of thechain A1 so as to mesh with the sprocket A2, as well as two smallmeshing teeth b formed at the outer circumferential side of the chain A1so as to mesh with the toothed pulley A3.

[0008] Plates A7 and A8 each have two meshing teeth c formed at theinner circumferential side of the chain A1 so as to mesh with thesprocket A2, as well as a flat back face d formed opposite to themeshing teeth c.

[0009] Notably, the meshing teeth c formed at the inner circumferentialside of the chain A1 and the teeth of the sprocket A2, which mesh withthe meshing teeth c, employ a standard tooth profile. By contrast, themeshing teeth b formed at the outer circumferential side of the chain A1and the teeth of the toothed pulley A3, which mesh with the meshingteeth b, employ a non-standard tooth profile.

[0010] The above conventional double-meshing-type silent chain employsthree kinds of link plates having different shapes. Thus, in a step ofmanufacturing plates, link plate dies corresponding to the differentlink plate shapes must be used. Also, in an assembling step, a largenumber of kinds of component parts must be handled and controlled. As aresult, manufacturing cost is high.

[0011] Also, since the profile of the meshing teeth formed at the outercircumferential side of the chain is smaller than the standard toothprofile, when a large load torque acts on the toothed pulley locatedoutside the chain, the toothed pulley disengages from the chain andslips along the chain. Thus, a maximum torque that can be transmitted tothe toothed pulley is smaller than that which can be transmitted to thesprocket located inside the chain. This significantly limits theselection of a device to be driven through engagement with the outercircumference side of the chain.

[0012] Further, the guide link plate has no meshing teeth at the innercircumferential side of the chain, but instead has the straight edgeportion at the inner circumferential side of the chain. Consequently,the guide link plate is relatively heavy, causing an increase in theweight of the entire chain. This causes an increase in impact energygenerated due to meshing engagement between the chain and the sprocketor between the chain and the toothed pulley when the chain travels,resulting in an increase in working noise.

[0013] Also, a heavy chain weight causes an increase in tension derivedfrom a centrifugal force produced when the chain travels, acceleratingwear of a shoe surface of a chain guide or the like as well aselongation of the chain. Particularly, when such a double-meshing-typesilent chain is used as a timing chain for an engine, timing drive ofthe engine may be adversely effected.

SUMMARY OF THE INVENTION

[0014] An object of the present invention is to provide adouble-meshing-type silent chain drive which solves the abovementionedproblems involved in the prior art, enables a reduction in manufacturingcost through improvement of productivity, and enables transmission of astrong driving force between a double-meshing-type silent chain and asprocket meshed with the chain along the outer circumference thereof.

[0015] Another object of the present invention is to provide a sprocketfor meshing with the double-meshing-type silent chain, which is capableof suppressing chain vibration while maintaining high transmissionefficiency.

[0016] To achieve the above object, the present invention provides adouble-meshing-type silent chain drive comprising a double-meshing-typesilent chain and a sprocket for meshing with the chain. The chainincludes link plates having the identical side profile. Each link platehas two meshing teeth and a flat back face formed opposite to themeshing teeth. Two kinds of links are alternately arranged in thelongitudinal direction of the chain, while the adjacent links areconnected by pins. In one kind of link, an odd number of the link platesare disposed in the width direction of the chain. In the other kind oflink, an even number of the link plates are disposed in the widthdirection of the chain. In each link, the link plates are oriented suchthat the meshing teeth of link plates located at widthwise opposite endsproject outwardly with respect to the chain and the meshing teeth of theremaining link plates project inwardly with respect to the chain.

[0017] In the double-meshing-type silent chain of the present invention,all of the link plates have the identical side profile. Also, theoutermost link plates of each link are oriented such that their meshingteeth project outwardly with respect to the chain. Thus, these outwardlyprojecting meshing teeth are meshed with a sprocket disposed outside thechain to thereby transmit power between the chain and the sprocket.

[0018] In each link, all the link plates except the outermost linkplates are oriented such that the meshing teeth project inwardly withrespect to the chain. These inwardly projecting meshing teeth are meshedwith a sprocket disposed inside the chain to thereby transmit powerbetween the chain and the sprocket.

[0019] Since all of the link plates have the identical side profile, thelink plates can be manufactured through use of a single kind of linkplate die. As compared to the case of a conventional chain of this kindcomposed of link plates having a plurality of side profiles, man-hoursrequired for control of component parts can be reduced, and erroneousassembly can be prevented, thereby greatly improving productivity.

[0020] In contrast to the case of a conventional silent chain, largeheavy guide plates having no teeth are not used, thereby reducing theweight of the entire chain.

[0021] Further, since meshing teeth which project outwardly with respectto the chain are profiled similarly to those which project inwardly withrespect to the chain, there can be increased a torque that can betransmitted between the chain and a sprocket disposed outside the chain.

[0022] Preferably, the double-meshing-type silent chain of the presentinvention is such that, in each link, the meshing teeth of some linkplates oriented in one direction project beyond the back faces of theremaining link plates oriented in an opposite direction.

[0023] In this case, the shoe face of a chain guide or that of atensioner lever can be brought into slidable contact with the back facesof the plates oriented outwardly with respect to the chain, while theopposite side faces of the shoe are guided along the inside faces of themeshing teeth of the opposed outermost link plates, which meshing teethproject outwardly beyond the plate back faces.

[0024] The sprocket may be a first-type sprocket for meshing with thedouble-meshing-type silent chain along the outer circumference thereof,wherein a plate support face is formed in each of meshing teeth of thesprocket so as to support the back faces of the link plates which areoriented outwardly with respect to the chain, during the sprocketmeshing with the link plates whose meshing teeth are oriented outwardlywith respect to the chain.

[0025] In the first-type sprocket, power transmission is achievedthrough engagement with the meshing teeth of the outermost link platesin each link. Also, the plate support face formed in each meshing toothof the sprocket abuts on the back faces of the link plates which areoriented outwardly with respect to the chain, to thereby partially beara reaction force of the running chain imposed on sprocket teeth and thusimprove sprocket durability. Further, the plate support faces serve as achain guide for guiding the back faces of link plates to therebysuppress chain vibration.

[0026] Since an existing standard sprocket can be used as the first-typesprocket by machining tip portions of sprocket teeth to form the platesupport face in each sprocket tooth, the first-type sprocket can bemanufactured at low cost and can be used with the double-meshing-typesilent chain of the present invention.

[0027] The sprocket may also be a second-type sprocket for meshing withthe double-meshing-type silent chain along the outer circumferencethereof, comprising a plate-back-face support element and two meshingelements. The plate-back-face support element has a cylindrical surfacethat abuts on the flat back faces of the link plates which are orientedoutwardly with respect to the chain. The meshing elements are integrallycoupled with the plate-back-face support element such that theplate-back-face support element is interposed between the meshingelements. Meshing teeth are formed on the circumferences of the meshingelements concentrically with the cylindrical surface of theplate-back-face support element so that the meshing elements can meshwith the link plates whose meshing teeth project outwardly with respectto the chain.

[0028] In the second-type sprocket, the two meshing elements havemeshing teeth which are formed on the circumferences and which areprofiled so as to completely mesh with outwardly projecting meshingteeth of the chain. Therefore, when the second-type sprocket is meshedwith the outer circumferential side of the double-meshing-type silentchain of the present invention, a large torque can be transmittedtherebetween.

[0029] Also, in the second-type sprocket, the plate-back-face supportelement has a continuous cylindrical surface for contact with back facesof link plates. The continuous cylindrical profile establishescontinuous and smooth contact with the back faces, thereby significantlysuppressing chain vibration and partially bearing a reaction force ofthe running chain imposed on sprocket teeth to thereby lessen sprocketteeth load. Thus, sprocket durability can be improved.

[0030] The sprocket may be a third-type sprocket for meshing with thedouble-meshing-type silent chain along the outer circumference thereof.The sprocket includes a meshing element having meshing teeth formed onan outer circumference thereof for meshing engagement with the meshingteeth of the link plates which are oriented inwardly with respect to thechain, and two plate-back-face support elements provided concentricallyon opposite sides of the meshing element and each having a cylindricalouter surface for abutment with the flat back faces of the link platesof the chain which are oriented inwardly with respect to the chain.

[0031] When the third-type sprocket is used for mesh with thedouble-meshing-type silent chain along the inner circumference thereof,the meshing teeth formed on the circumference of the meshing element arein mesh with the meshing teeth of the chain which are oriented inwardlywith respect to the chain to achieve power transmission between thesprocket and the chain. At the same time, the respective cylindricalouter surfaces of the plate-back-face support elements provided onopposite sides of the meshing element abut on the flat back faces of thelink plates which are oriented inwardly with respect to the chain tothereby support or bear reaction from the chain.

[0032] In the third-type sprocket, while the meshing teeth of themeshing element mesh with the meshing teeth of the chain orientedinwardly with respect to the chain to achieve power transmission, theplate-end-face support elements smoothly guide and support the flat backfaces of the link plates to thereby achieve the function of a chainguide. Vibrations resulting from polygonal movement of the chain can besuppressed to thereby stabilize the travel condition of the chain andlower the operation noise.

[0033] It is preferable that when the cylindrical outer surface of eachof the plate-back-face support elements is in abutment with the flatback faces of the link plates, the meshing teeth of the meshing elementmesh with the meshing teeth of the opposing link plates at a positionoffset from a meshing pitch circle of the meshing teeth of the meshingelement in a radial outward direction of the sprocket. With thisarrangement, the cylindrical outer surfaces of the plate-end-facesupport elements forcibly displace the back faces of the link plates ina radial outward direction before the meshing teeth of the meshingelement mesh with the teeth of the chain. With this displacement, themeshing teeth of the sprocket mesh with the meshing teeth of the chainat a position located outside the meshing pitch circle of the meshingteeth of the sprocket. Such meshing is particularly effective to reducethe load in the radial direction of the sprocket.

[0034] The sprocket may be a fourth-type sprocket which comprises aplate-back-face support element having a cylindrical outer surface forabutment with the flat back faces of the link plates of the chain thatare oriented outwardly with respect to the chain, and two meshingelements provided concentrically on opposite sides of the plate-end-facesupport element and each having meshing teeth formed on an outercircumference thereof for meshing engagement with the meshing teeth ofthe link plates of the chain which are oriented outwardly with respectto the chain. The cylindrical outer surface of the plate-back-facesupport element is in abutment with the flat back faces of the linkplates, and the meshing teeth of each of the meshing elements mesh withthe meshing teeth of the opposing link plates at a position offset froma meshing pitch circle of the meshing teeth of the meshing elements in aradial outward direction of the sprocket.

[0035] In the fourth-type sprocket, the cylindrical outer surface of theplate-end-face support element forcibly displaces the back faces of thelink plates in a radial outward direction before the meshing teeth ofthe meshing elements mesh with the teeth of the chain. With thisdisplacement, the meshing teeth of the sprocket mesh with the meshingteeth of the chain at a position located outside the meshing pitchcircle of the meshing teeth of the sprocket. Such meshing isparticularly effective to reduce the load in the radial direction of thesprocket.

[0036] The sprocket may be a fifth-type sprocket for meshing with adouble-meshing-type silent chain, which comprises two meshing elementseach having teeth formed on an outer circumference thereof for meshingengagement with the meshing teeth of the link plates of the chain whichare oriented outwardly with respect to the chain, a buffer-ring supportelement having a cylindrical outer surface and concentrically andintegrally joining the two meshing elements, and a buffer ring having aninside diameter larger than the outside diameter of the buffer-ringsupport element and being floatingly fitted around the cylindrical outersurface of the buffer-ring support element while the buffer ring isprevented from moving in the axial direction between the two meshingelements. The buffer ring has an outer peripheral surface adapted to bein abutment with opposing flat back faces of link plates at positions infront and in rear of a meshing position at which the meshing teeth ofthe link plates are in mesh with the meshing teeth of the meshingelements. At the meshing position, the outer peripheral surface of thebuffer ring is separated from the flat back faces of the link plates andan inner peripheral surface of the buffer ring is in abutment with thecylindrical outer surface of the buffer-ring support element.

[0037] When the fifth-type sprocket is used for meshing with thedouble-meshing-type silent chain along the outer circumference thereof,the outer peripheral surface of the buffer ring disposed between themeshing elements is first brought into abutment with the flat end facesof the link plates of the chain.

[0038] When the back faces of the link plates impinge on the outerperipheral surface of the buffer ring, the buffer ring is flexed orotherwise deformed in a floating manner around the buffer-ring supportmember to thereby absorb impact energy created at a collision.Thereafter, as the chain advances, the meshing teeth of the outermostlink plates of each link reach the meshing position, the outerperipheral surface of the buffer ring disengages from the back faces ofthe link plates. At the meshing position, the inner peripheral surfaceof the buffer ring abuts on the cylindrical outer surface of thebuffer-ring support element.

[0039] As the chain further advances, the outer peripheral surface ofthe buffer ring comes again into abutment with the opposing back facesof the link plates to thereby guide the chain such that the engagementbetween the meshing teeth of each meshing element and the meshing teethof the corresponding link plates is released.

[0040] In the fifth-type sprocket, since the outer peripheral surface ofthe buffer ring fitted around the buffer-ring support element abuts onthe back faces of the link plates in advance to the mutual meshingbetween the meshing teeth of the sprocket and the meshing teeth of thechain, vibrations of the chain arising from polygonal movement of thechain as the chain moves past the sprocket can be suppressed. At thesame time, collision between the meshing teeth of the sprocket and themeshing teeth of the chain can be absorbed with the result that theoperation noise of the chain while running is considerably reduced.

[0041] As the sprocket rotates, the buffer ring is caused to oscillateor wobble around the buffer-ring support element while it is rotatingabout its own axis. Thus, the position of collision between the meshingteeth of the sprocket and the meshing teeth of the chain changes atrandom, so that excess local wear of the tooth surfaces can beprevented.

[0042] Additionally, a lubricating oil supplied externally is guided bythe buffer ring between the mutually intermeshing teeth of the chain andsprocket with the result that the teeth are protected against wear andfatigue and wear elongation of the chain is minimized.

[0043] The sprocket may be a sixth-type sprocket used for meshing with adouble-meshing-type silent chain along the inner circumference thereof,which comprises a meshing element having teeth formed on an outercircumference thereof for meshing engagement with meshing teeth of linkplates of the chain which are oriented inwardly with respect to thechain, two buffer-ring support elements each having a cylindrical outersurface and provided concentrically on opposite sides of the meshingelement, and two buffer rings each having an inside diameter larger thanthe outside diameter of the buffer-ring support elements and each beingfloatingly fitted around the cylindrical outer surface of one of thebuffer-ring support elements while the buffer rings are prevented frommoving in the axial direction relative to the corresponding buffer-ringsupport elements. The buffer rings each have an outer peripheral surfaceadapted to be in abutment with opposing flat back faces of link platesat positions in front and in rear of a meshing position at which themeshing teeth of the link plates are in mesh with the meshing teeth ofthe meshing element. At the meshing position, the outer peripheralsurface of each of the buffer rings is separated from the flat backfaces of the link plates and an inner peripheral surface of each of thebuffer rings is in abutment with the cylindrical outer surface of one ofthe buffer-ring support elements.

[0044] When the sixth-type sprocket is used for meshing with thedouble-meshing-type silent chain along the inner circumference thereof,the outer peripheral surfaces of the buffer rings disposed on oppositesides of the meshing element are first brought into abutment with theflat end faces of the link plates of the chain.

[0045] When the back faces of the link plates impinge on the outerperipheral surfaces of the buffer rings, the buffer rings are flexed orotherwise deformed in a floating manner around the buffer-ring supportmembers to thereby absorb impact energy created at a collision.Thereafter, as the chain advances, the meshing teeth of the outermostlink plates of each link reach the meshing position, the outerperipheral surfaces of the buffer rings disengage from the back faces ofthe link plates. At the meshing position, the inner peripheral surfacesof the buffer rings abut on the cylindrical outer surfaces of thebuffer-ring support elements.

[0046] As the chain further advances, the outer peripheral surfaces ofthe buffer rings come again into abutment with the opposing back facesof the link plates and guide the chain such that the engagement betweenthe meshing teeth of the meshing element and the meshing teeth of thecorresponding link plates is released.

[0047] The sixth-type sprocket has substantially the same advantageouseffects as those of the fifth-type sprocket described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Various other objects, features and many of the attendantadvantages of the present invention will be readily appreciated as thesame becomes better understood by reference to the following detaileddescription of the preferred embodiments when considered in connectionwith the accompanying drawings, in which:

[0049]FIG. 1 is a side view showing an embodiment of adouble-meshing-type silent chain according to the present invention;

[0050]FIG. 2 is a plan view showing the double-meshing-type silent chainof FIG. 1;

[0051]FIG. 3 is a side view showing a first embodiment of a sprocketaccording to the present invention for meshing with adouble-meshing-type silent chain along the outer circumference thereof;

[0052]FIG. 4 is a partially sectional view taken along the line A-A ofFIG. 3;

[0053]FIG. 5 is a side view showing a second embodiment of the sprocketaccording to the present invention for meshing with thedouble-meshing-type silent chain along the outer circumference thereof;

[0054]FIG. 6 is a partially sectional view taken along the line B-B ofFIG. 5;

[0055]FIG. 7 is a side view showing a third embodiment of the sprocketaccording to the present invention for meshing with adouble-meshing-type silent chain along the outer circumference thereof;

[0056]FIG. 8 is a partially sectional view taken along the line C-C ofFIG. 7;

[0057]FIG. 9 is a partially sectional view showing a fourth embodimentof the sprocket according to the present invention for meshing with adouble-meshing-type silent chain along the outer circumference thereof;

[0058]FIG. 10 is a fragmentary side view showing a fifth embodiment ofthe sprocket according to the present invention which is in mesh with adouble-meshing-type silent chain along the outer circumference thereof;

[0059]FIG. 11 is a fragmentary side view showing for comparativepurposes the condition in which the chain and the sprocket of FIG. 10are in mesh with each other with the cylindrical outer surface of aplate-back-face support element of the sprocket being separated from theback faces of the link plates of the chain;

[0060]FIG. 12 is a fragmentary side view showing a sixth embodiment ofthe sprocket according to the present invention which is in mesh with adouble-meshing-type silent chain along the outer circumference thereof;

[0061]FIG. 13A is a partially sectional view taken along the line X-X ofFIG. 12;

[0062]FIG. 13B is a partially sectional view taken along the line Y-Y ofFIG. 12;

[0063]FIG. 13C is a partially sectional view taken along the line Z-Z ofFIG. 12;

[0064]FIG. 14 is a fragmentary side view showing a seventh embodiment ofthe sprocket according to the present invention which is in mesh with adouble-meshing-type silent chain along the inner circumference thereof;

[0065]FIG. 15 is a partially sectional view taken along the line D-D ofFIG. 14;

[0066]FIG. 16 is a sectional view showing an eighth embodiment of thesprocket according to the present invention which is in mesh with adouble-meshing-type silent chain along the inner circumference thereof;

[0067]FIG. 17 is a view showing a conventional double-meshing-typesilent chain; and

[0068]FIG. 18 is a view showing a link plate configuration of the silentchain of FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] Embodiments of the present invention will next be described indetail with reference to the drawings. FIG. 1 is a side view showing anembodiment of a double-meshing-type silent chain according to thepresent invention. FIG. 2 is a plan view of the silent chain. In FIGS. 1and 2, a double-meshing-type silent chain (hereinafter, referred tosimply as a “chain” ) 1 includes link plates 2A, 2B, 2C, and 2D havingthe identical side profile.

[0070] The link plates 2A, 2B, 2C, and 2D each have two meshing teeth Tand a flat back face S formed opposite to the meshing teeth T. Themeshing teeth T have a tooth profile similar to that of a standardsilent chain.

[0071] In the chain 1, two kinds of links are alternately arranged inthe longitudinal direction of the chain 1, while the adjacent links areconnected by pins 3. One kind of link is composed of an odd number oflink plates, specifically three of link plates 2C and two of the linkplates 2A which are disposed such that the three link plates 2C areinterposed between the two link plates 2A. The other kind of link iscomposed of an even number of link plates, specifically two of the linkplates 2D and two of the link plates 2B which are disposed such that thetwo link plates 2D are interposed between the two link plates 2B.

[0072] The links are connected endlessly, while the outermost linkplates 2A and 2B are oriented such that the meshing teeth T projectoutwardly with respect to the chain 1 and while the link plates 2C and2D interposed between the link plates 2A and between the link plates 2B,respectively, are oriented such that the meshing teeth T projectinwardly with respect to the chain 1.

[0073] The link plates 2A and 2B, whose meshing teeth T projectoutwardly with respect to the chain 1, and the link plate 2D, which ispresent in the same link as that in which the link plate 2B is present,have the identical thickness. The link plate 2C is thinner than the linkplates 2A, 2B, and 2D. Thus, a uniform tensile strength is imparted tothe links.

[0074] According to the present embodiment, in each link, link platesare connected by the pin 3 such that the meshing teeth T of some linkplates oriented in one direction project beyond the back faces S of theremaining link plates oriented in an opposite direction. Thus, the shoeface of a chain guide or tensioner lever can be brought into slidablecontact with the back faces S of the link plates 2C and 2D orientedoutwardly with respect to the chain 1, while the opposite side faces ofthe shoe are guided along the inner faces of the meshing teeth T of theopposed outermost link plates 2B, which meshing teeth T projectoutwardly beyond the plate back faces S of the link plates 2C and 2D.

[0075] Also, an unillustrated sprocket located inside and meshed withthe chain 1 is guided by the link plates 2B, whose back faces S areoriented inwardly with respect to the chain 1. Specifically, the sidefaces of sprocket teeth are guided along the inner faces of the opposedlink plates 2B. Thus, the link plates 2B serve as guide plates employedin a conventional silent chain.

[0076] Notably, in the same link, the link plates 2A (2B) and 2C (2D)may be connected by the pin 3 such that the meshing teeth T of the linkplates 2A (2B) are aligned with or recessed from the back faces S of theoppositely oriented link plates 2C (2D). This feature enables a chainguide or a tensioner lever to have a shoe wider than the width of thechain 1.

[0077]FIG. 3 is a side view showing a first embodiment of a sprocketaccording to the present invention for meshing with adouble-meshing-type silent chain along the outer circumference thereof.FIG. 4 is a partially sectional view taken along the line A-A of FIG. 3.As shown in FIGS. 3 and 4, a sprocket 4 according to the firstembodiment is disposed outside the chain 1.

[0078] Meshing teeth t of the sprocket 4 have a standard tooth profileso as to be compatible with the meshing teeth T of the chain 1. Awidthwise central portion of the tip region of each meshing tooth t iscut away to form a plate support face K. The plate support face K isformed as a portion of a cylindrical surface concentric with therotation axis of the sprocket 4.

[0079] The sprocket 4 is slightly wider than the maximum width of thechain 1. An existing standard sprocket having standard teeth for meshingwith a silent chain can be readily used as the sprocket 4 by simplymachining tip portions of sprocket teeth.

[0080] Portions of each meshing tooth t located at opposite sides of theplate support face K mesh with the meshing teeth T of the link plates 2Aand 2B disposed at opposite sides of the chain 1, thereby transmittingtorque between the chain 1 and the sprocket 4 as in the case of aconventional silent chain.

[0081] During such torque transmission, the plate support faces K abuton the back faces S of the link plates 2C and 2D to thereby serve asguides for the back faces S. At the same time, torque is partiallytransmitted between the chain 1 and the sprocket 4 in the form of africtional force generated between the back faces S and the platesupport faces K. Also, the plate support faces K partially bear areaction force of the running chain 1 imposed on the sprocket teeth t,thereby contributing toward improving durability of the sprocket 4.

[0082]FIG. 5 is a side view showing a second embodiment of the sprocketaccording to the present invention for meshing with adouble-meshing-type silent chain along the outer circumference thereof.FIG. 6 is a partially sectional view taken along the line B-B of FIG. 5.As shown in FIGS. 5 and 6, in a sprocket 4′ according to the secondembodiment, a plate support face K′, which abuts on the back faces S ofthe link plates 2C and 2D, is formed on each of meshing teeth t of thesprocket 4′ at a tip portion across the entire width of the meshingtooth t. As in the case of the sprocket 4, an existing standard sprockethaving standard teeth for meshing with a silent chain can be used as thesprocket 4′ by simply machining tip portions of sprocket teeth over theentire teeth width.

[0083]FIG. 7 is a side view showing a third embodiment of the sprocketaccording to the present invention for meshing with adouble-meshing-type silent chain along the outer circumference thereof.FIG. 8 is a partially sectional view taken along the line C-C of FIG. 7.As in the case of the sprocket 4, a sprocket 14 according to the thirdembodiment is meshed with the chain 1 along the outer circumferencethereof.

[0084] The sprocket 14 is composed of a plate-back-face support element14A and two meshing elements 14B. The plate-back-face support element14A has a cylindrical surface R for abutment with the back faces S ofthe link plates 2C and 2D which are oriented outwardly with respect tothe chain 1. The plate-back-face support element 14A is interposedbetween and coaxially coupled with the two meshing elements 14B by meansof, for example, unillustrated screws so that the plate-back-facesupport element 14A and the two meshing elements 14B rotate as a singleunit.

[0085] Meshing teeth t′ are formed on the two meshing elements 14B alongthe outer circumferences such that the meshing teeth t′ of one meshingelement 14B are arranged in the same phase as the meshing teeth t′ ofthe other meshing element 14B. The meshing teeth t′ have a standardtooth profile of a conventional sprocket for use with a silent chain soas to mesh with the meshing teeth T of the outermost link plates 2A and2B of the chain 1.

[0086] Thus, the state of engagement between a conventional silent chainand a sprocket can be similarly established between the meshing teeth t′and the outwardly projecting meshing teeth T of the chain 1 to therebyenable transmission of strong torque therebetween.

[0087] While the meshing elements 14B are meshed with the chain 1, thecylindrical surface R of the plate-back-face support element 14A is inabutment with the back faces S of the link plates 2C and 2D so as toguide and support the back faces S. At the same time, a frictional forcegenerated between the back faces S and the cylindrical surface Restablishes auxiliary torque transmission between the chain 1 and thesprocket 14.

[0088] Notably, in the sprocket 14, only the two meshing elements 14Bmay be made of metal such as steel, and the plate-back-face supportelement 14A is made of a resin material. In this case, the resinmaterial absorbs impact which is generated between the cylindricalsurface R of the plate-back-face support element 14A and the back facesS of the link plates 2C and 2D due to meshing between the sprocket 14and the chain 1. Thus, meshing noise can be reduced.

[0089] When the plate-back-face support element 14A is to be made of ametallic material, the plate-back-face support element 14A and themeshing elements 14B may be integrally manufactured into a single unitby a method in which a metallic power is compacted and then sintered.

[0090]FIG. 9 is a partially sectional view showing a fourth embodimentof the sprocket according to the present invention for meshing with adouble-meshing-type silent chain along the outer circumference thereof.A sprocket 24 of the fourth embodiment as shown in FIG. 9 is differentfrom the sprocket 14 of the third embodiment only in the structure of aplate-back-face support element.

[0091] Specifically, in the sprocket 24, a plate-back-face supportelement 24A is composed of a cylindrical base 24C made of steel and abuffer ring 24D made of rubber. The buffer ring 24D has a cylindricalouter surface R for abutment with the back faces S of the link plates 2Cand 2D.

[0092] Two meshing members 24B, between which the plate-back-facesupport element 24A is interposed, have the identical shape as that ofthe meshing members 14B of the sprocket 14.

[0093] While the sprocket 24 is meshed with the chain 1, the back facesS of the link plates 2C and 2D abut on the cylindrical surface R of thebuffer ring 24D, thereby yielding large impact-absorbing effect as wellas noise-absorbing effect. Thus, vibrations of the chain 1 can besuppressed, and large noise reduction effect can be yielded.

[0094] Since large friction is generated between the back faces S of thelink plates 2C and 2D and the cylindrical surface R of the buffer ring24D, there can be increased auxiliary torque transmission between theback faces S and the cylindrical surface R. Thus, through torquetransmission between the meshing elements 24B and the link plates 2A and2B as well as the auxiliary torque transmission, strong torque can betransmitted between the chain 1 and the sprocket 24.

[0095] In the sprocket 24, in order to reduce the number of componentparts and assembling man-hours, either one of the meshing elements 24Bmay be integrally formed with the cylindrical base 24C, and the othermeshing element 24B may be manufactured independently.

[0096]FIG. 10 is a fragmentary side view showing a fifth embodiment ofthe sprocket according to the present invention for meshing with adouble-meshing-type silent chain along the outer circumference thereof.A sprocket 141 is so designed as to improve the meshing characteristicsof the sprocket 14 of the third embodiment shown in FIGS. 7 and 8. Thestructure of the sprocket 14′ itself is the same as the structure of thesprocket 14.

[0097] In the sprocket 14′ shown in FIG. 10, the outside diameter of acylindrical outer surface R of a plate-back-face support element 14′A isslightly greater than that of the cylindrical surface R of theplate-back-face support element 14A of the sprocket 14 so that meshingteeth t of each meshing element 14′B is meshed with meshing teeth T ofthe link plates 2A, 2B at positions offset or displaced from a meshingpitch circle P of the sprocket 14′ toward a radial outward side thereofwhen the plate-back-face support element 14′A is in abutment with theback faces S of the link plates 2C, 2D. The meshing teeth t have astandard tooth profile.

[0098] With this construction, when the chain 1 comes into meshingengagement with the sprocket 14′, the cylindrical surface R forciblydisplaces the back faces S of the link plates 2C, 2D in the radialoutward direction. Accordingly, the most part of a load acting from thechain 1 in a radial inward direction of the sprocket 14′ is born by thecylindrical surface R of the plate-back-face support element 14′A whilebeing in abutment with the back faces S of the link plates 2C, 2D.

[0099] As a result, loads on the meshing teeth T of the link plates 2A,2B and the meshing teeth t of the sprocket 14′ are decreased, and theforce acting between the meshing teeth t of the sprocket 14′ and themeshing teeth T of the link plates 2A, 2B can be effectively used forpower transmission between the sprocket 14′ and the chain 1.

[0100] Thus, wear of the meshing teeth t and the meshing teeth T isdecreased, thereby increasing the durability of the sprocket 14′ and thechain 1.

[0101]FIG. 11 shows for comparative purposes the condition in which dueto its smaller outside diameter than the cylindrical surface R shown inFIG. 10, a cylindrical outer surface R′ of the plate-back-face supportelement 14′A of the sprocket 14′ is separated from the back faces S ofthe link plates 2C, 2D. Under such condition, when the chain 1 movesinto meshing engagement with the sprocket 14′, tooth faces of themeshing teeth T of the link plates 2A, 2B are wedged between the toothfaces of the meshing teeth t of the sprocket 14′ by a tension acting onthe chain 1. This engagement creates a great stress in the vicinity ofthe respective tooth faces of the meshing teeth t, T which will resultin accelerated wear of the meshing teeth t, T and generation of greatoperation noises.

[0102] The number of meshing teeth T of the chain 1 which areconcurrently meshed with the meshing teeth t of the sprocket 14′ issmaller on the outer circumference side than on the innercircumferential side of the chain 1. Accordingly, in order to reduce theload to be born by the meshing teeth t, T, it is desirable that when thechain 1 is moved into meshing engagement with the sprocket 14′, thecylindrical outer surface R of the plate-back-face support element 14′Alifts up the back faces S of the link plates 2C, 2D and thus displacesthe meshing position between the meshing teeth T of the chain 1 and themeshing teeth t of the sprocket 14′ in a radial outward direction of thepitch circle P, as shown in FIG. 10.

[0103]FIG. 12 is a side view showing a sixth embodiment of the sprocketaccording to the present invention for meshing with adouble-meshing-type silent chain. FIGS. 13A, 13B and 13C are partiallysectional views taken along the line X-X, Y-Y and ZZ, respectively, ofFIG. 12. A sprocket 34 shown in these figures includes a buffer-ringsupport element 34A having a cylindrical outer surface F, and a pair ofmeshing elements 34B connected integrally with opposite sides of thebuffer-ring support element 34A.

[0104] The meshing elements 34B are concentric with the buffer-ringsupport element 34A and each have meshing teeth t formed on thecircumference of the meshing element 34B for meshing engagement withteeth T of link plates 2A, 2B projecting toward the outer circumferenceside of the chain 1.

[0105] The outer surface F of the buffer-ring support element 34A has anoutside diameter which is slightly smaller than a root circle of themeshing teeth t formed on the respective circumferences of the meshingelements 34B. A buffer ring 34C is floatingly fitted around the outersurface F of the buffer-ring support element 34A.

[0106] As shown in FIG. 12, when the chain 1 is in mesh with thesprocket 34 along the outer circumference thereof, the buffer ring 34Cis forced on its outer peripheral surface by the flat back faces S ofthe link plates 2C, 2D so that the center of the buffer ring 34C isoffset from the center of the sprocket 34 until an inner peripheralsurface of the buffer ring 34C is held in abutment with the outersurface F of the buffer-ring support element 34A along itscircumferential portion extending in the vicinity of the line Z-Zposition of FIG. 12 so as to achieve a line contact state between thebuffer ring 34C and the buffer-ring support element 34A.

[0107] When the chain 1 moves into meshing engagement with the sprocket34, the outer peripheral surface of the buffer ring 34C comes in contactwith the flat back faces D of the link plates 2C, 2D at the X-X lineposition of FIG. 12 before the meshing teeth T of the left and rightoutermost link plates 2A and 2B of the chain 1 mesh with meshing teeth tof the pair of meshing elements 34B, as shown in FIG. 13A.

[0108] In this instance, since the buffer ring 34C is in abutment withthe outer surface F of the buffer-ring support element 34A under theline-contact state or condition along its limited circumferentialportion, the buffer ring 34C, upon abutment with the flat back faces Sof the link plates 2A, 2B, is readily able to flex or otherwise deformin a floating manner around the buffer-ring support element 34A tothereby absorb impact energy at collision between the buffer ring 34Cand the link plates 2A, 2B. The impact can thus be relieved.

[0109] At the line Y-Y position of FIG. 12, as shown in FIG. 13B, theouter surface of the buffer ring 34C is spaced from the back faces S ofthe link plates 2C, 2D. In place of this spacing, the meshing teeth Tformed on the outermost link plates 2A, 2B are in mesh with and thussupported by the meshing teeth t of the meshing elements 34B of thesprocket 34.

[0110] After passing through the line Z-Z position of FIG. 12, the outersurface of the buffer ring 34C comes again in contact with the backfaces S of the link plates 2C, 2D and forces the chain 1 in a radialoutward direction of the sprocket 34 to thereby disengage the meshingteeth T of the chain 1 from the meshing teeth t of the sprocket 34.

[0111] During that time, the buffer ring 34C while rotating in unisonwith the sprocket 34 catches or takes thereinto a lubricating oilsupplied externally and subsequently feeds the lubricating oil betweenthe mutually intermeshing teeth t, T of the sprocket 34 and chain 1.

[0112] The buffer ring 34C is formed from a metallic material such assteel in view of the strength. To provide an improved impact relievingeffect and a reduced operation noise, the surface of the buffer ring 34Cmay be covered with a coating layer of rubber or resin material. Thebuffer ring 34C as a whole may be formed from a non-metallic materialsuch as rubber or synthetic resin provided that the desired strength canbe maintained.

[0113]FIG. 14 is a fragmentary side view showing a seventh embodiment ofthe sprocket according to the present invention which is in mesh with adouble-meshing-type silent chain along the inner circumference thereof.FIG. 15 is a partially sectional view taken along the line D-D of FIG.14.

[0114] A sprocket 44 in this embodiment includes a meshing element 44Ahaving meshing teeth t formed on its circumference for meshingengagement with meshing teeth T of the chain 1 which are oriented towardthe inner circumference side of the chain 1, and a pair ofplate-back-face support elements 44B disposed on opposite sides of themeshing element 44 a in concentric relation to the meshing element 44 a.The plate-back-face support elements 44B each have a cylindrical outersurface R.

[0115] The cylindrical outer surfaces R of the plate-back-face supportelements 44B have a diameter slightly smaller than the diameter of anaddendum circle of the meshing teeth t of the sprocket 44, so that whenthe meshing teeth T of the chain 1 come in meshing engagement with themeshing teeth t of the sprocket 44, the cylindrical outer surfaces Rabut on the flat back faces S of the outermost link plates 2A, 2B ineach link of the chain 1. Thus the cylindrical outer surface R of theplate-back-face support elements 44B supports or bears a load appliedfrom the chain 1 in a radial inward direction and suppresses vibrationof the chain 1.

[0116] The diameter of the respective cylindrical outer surfaces R ofthe plate-back-face support elements 44B is preferably determined suchthat when the cylindrical outer surfaces R are in abutment with the backfaces S of the link plates 2A, 2B, the meshing teeth t of the sprocket44 are in mesh with the meshing teeth T of the link plates 2C, 2D on aradial outward side of the meshing pitch circle of the meshing teeth t.

[0117] With this arrangement, before the meshing teeth T of the chain 1come into meshing engagement with the meshing teeth t of the sprocket44, the cylindrical outer surfaces R of the plate-back-face supportelements 44B lift up the back faces S of the link plates 2A, 2B and thusdisplace the back faces S in a radial outward direction. With thisdisplacement of the link plates back faces S, since the meshing teeth tof the sprocket 44 mesh with the meshing teeth T of the chain 1 on theoutside of the meshing pitch circle, a load acting between the meshingteeth t of the sprocket 44 and the meshing teeth T of the chain 1 in aradial direction can be considerably reduced.

[0118] Although in the illustrated embodiment the meshing element 44Aand the plate-back-face support elements 44B are formed integrally froma single material, they may be produced separately from each other andthen assembled together to form a sprocket.

[0119]FIG. 16 is a sectional view showing an eighth embodiment of thesprocket according to the present invention which is in mesh with adouble-meshing-type silent chain along the inner circumference thereof.A sprocket 54 of this embodiment includes a meshing element 54A havingmeshing teeth t formed on its circumference for meshing engagement withmeshing teeth T of link plates 2C, 2D of the chain 1, and a pair ofbuffer-ring support elements 54B provided concentrically on oppositesides of the meshing element 54A and each having a cylindrical outersurface F.

[0120] A buffer ring 54C has an inside diameter larger than the outsidediameter of the buffer-ring support elements 54B and is floatinglyfitted around each of the buffer-ring support elements 54B. Ananti-displacement flange 54D is attached to each of the opposite endfaces of the buffer-ring support elements 54B so as to preventdisplacement of each buffer ring 54C in the axial direction of thesprocket 53 between one of the anti-displacement flanges 54D and themeshing element 54A.

[0121] In the sprocket 54 of this embodiment, the buffer rings 54Cprovided on opposite sides of the meshing teeth 54A operate in the samemanner as the buffer ring 34C of the sprocket 34 of the sixth embodimentshown in FIGS. 12 and 13A-13C and thus can absorb collision between themutually intermeshing surfaces when engagement between the meshing teetht of the sprocket 54 and the meshing teeth T on the inner circumferenceside of the chain 1 occurs.

[0122] Although in the illustrated embodiment the anti-displacementflanges 54D are attached to the opposite end faces of the buffer-ringsupport elements 54B to prevent the buffer rings 54C from displacing offthe buffer-ring support elements 54B, the anti-displacement flanges 54Dmay be attached to a rotating shaft J in sandwiching relation to thesprocket 54 which is mounted on the rotating shaft J.

[0123] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent invention may be practiced otherwise than as specificallydescribed herein.

What is claimed is:
 1. A double-meshing-type silent chain drivecomprising: a double-meshing-type silent chain including first links andsecond links alternately arranged in the longitudinal direction of saidchain, each of said first links being composed of an odd number of linkplates disposed in the width direction of said chain, and each of saidsecond links being composed of an even number of link plates disposed inthe width direction of said chain, and a plurality of pins each adaptedto connect adjacent two links with each other, wherein the link platesof said first links and the link plates of said second links have anidentical side profile such that two meshing teeth are formed at oneside and a flat back face is formed at the opposite side, and the linkplates in each of said first and second links are oriented such that themeshing teeth of link plates located at widthwise opposite ends projectoutwardly with respect to the chain and the meshing teeth of theremaining link plates project inwardly with respect to the chain; and asprocket for meshing with a double-meshing-type silent chain, saidsprocket including a meshing element having meshing teeth formed on anouter circumference thereof for meshing engagement with said meshingteeth of said link plates which are oriented inwardly with respect tothe chain, and two plate-back-face support elements providedconcentrically on opposite sides of said meshing element and each havinga cylindrical outer surface for abutment with said flat back faces ofthe link plates of the chain which are oriented inwardly with respect tothe chain.
 2. A double-meshing-type silent chain drive according toclaim 1, wherein, in each link, the meshing teeth of some link platesoriented in one direction project beyond the back faces of the remaininglink plates oriented in an opposite direction.
 3. A double-meshing-typesilent chain drive according to claim 1, wherein when said cylindricalouter surface of each of said plate-back-face support elements is inabutment with said flat back faces of the link plates, said meshingteeth of said meshing element mesh with the meshing teeth of theopposing link plates at a position offset from a meshing pitch circle ofsaid meshing teeth of said meshing element in a radial outward directionof said sprocket.
 4. A double-meshing-type silent chain drive accordingto claim 1, wherein said meshing element and said two plate-back-facesupport elements are integral with each other.
 5. A double-meshing-typesilent chain drive comprising: a double-meshing-type silent chainincluding first links and second links alternately arranged in thelongitudinal direction of said chain, each of said first links beingcomposed of an odd number of link plates disposed in the width directionof said chain, and each of said second links being composed of an evennumber of link plates disposed in the width direction of said chain, anda plurality of pins each adapted to connect adjacent two links with eachother, wherein the link plates of said first links and the link platesof said second links have an identical side profile such that twomeshing teeth are formed at one side and a flat back face is formed atthe opposite side, and the link plates in each of said first and secondlinks are oriented such that the meshing teeth of link plates located atwidthwise opposite ends project outwardly with respect to the chain andthe meshing teeth of the remaining link plates project inwardly withrespect to the chain; and a sprocket for meshing with adouble-meshing-type silent chain, said sprocket including aplate-back-face support element having a cylindrical outer surface forabutment with said flat back faces of the link plates of the chain thatare oriented outwardly with respect to the chain, and two meshingelements provided concentrically on opposite sides of saidplate-end-face support element and each having meshing teeth formed onan outer circumference thereof for meshing engagement with said meshingteeth of said link plates of the chain which are oriented outwardly withrespect to the chain, wherein when said cylindrical outer surface ofsaid plate-back-face support element is in abutment with the flat backfaces of the link plates, said meshing teeth of each of said meshingelements mesh with the meshing teeth of the opposing link plates at aposition offset from a meshing pitch circle of said meshing teeth ofsaid meshing elements in a radial outward direction of said sprocket. 6.A double-meshing-type silent chain drive according to claim 5, wherein,in each link, the meshing teeth of some link plates oriented in onedirection project beyond the back faces of the remaining link platesoriented in an opposite direction.
 7. A double-meshing-type silent chaindrive comprising: a double-meshing-type silent chain including firstlinks and second links alternately arranged in the longitudinaldirection of said chain, each of said first links being composed of anodd number of link plates disposed in the width direction of said chain,and each of said second links being composed of an even number of linkplates disposed in the width direction of said chain, and a plurality ofpins each adapted to connect adjacent two links with each other, whereinthe link plates of said first links and the link plates of said secondlinks have an identical side profile such that two meshing teeth areformed at one side and a flat back face is formed at the opposite side,and the link plates in each of said first and second links are orientedsuch that the meshing teeth of link plates located at widthwise oppositeends project outwardly with respect to the chain and the meshing teethof the remaining link plates project inwardly with respect to the chain;and a sprocket for meshing with a double-meshing-type silent chain, saidsprocket including two meshing elements each having teeth formed on anouter circumference thereof for meshing engagement with said meshingteeth of the link plates which are oriented outwardly with respect tothe chain, a buffer-ring support element having a cylindrical outersurface and concentrically and integrally joining said two meshingelements, and a buffer ring having an inside diameter larger than theoutside diameter of said buffer-ring support element and beingfloatingly fitted around said cylindrical outer surface of saidbuffer-ring support element while said buffer ring is prevented frommoving in the axial direction between said two meshing elements, whereinsaid buffer ring has an outer peripheral surface adapted to be inabutment with said flat back faces of the link plates at positions infront and in rear of a meshing position at which said meshing teeth ofthe link plates are in mesh with said meshing teeth of said meshingelements, and at said meshing position, said outer peripheral surface ofsaid buffer ring is separated from said flat back faces of the linkplates and an inner peripheral surface of said buffer ring is inabutment with said cylindrical outer surface of said buffer-ring supportelement.
 8. A double-meshing-type silent chain drive according to claim7, wherein, in each link, the meshing teeth of some link plates orientedin one direction project beyond the back faces of the remaining linkplates oriented in an opposite direction.
 9. A double-meshing-typesilent chain drive according to claim 7, wherein said buffer ring isformed from a metallic material.
 10. A double-meshing-type silent chaindrive according to claim 7, wherein said buffer ring is formed from anonmetallic material, said non-metallic material including rubber and aresin material.
 11. A double-meshing-type silent chain drive comprising:a double-meshing-type silent chain including first links and secondlinks alternately arranged in the longitudinal direction of said chain,each of said first links being composed of an odd number of link platesdisposed in the width direction of said chain, and each of said secondlinks being composed of an even number of link plates disposed in thewidth direction of said chain, and a plurality of pins each adapted toconnect adjacent two links with each other, wherein the link plates ofsaid first links and the link plates of said second links have anidentical side profile such that two meshing teeth are formed at oneside and a flat back face is formed at the opposite side, and the linkplates in each of said first and second links are oriented such that themeshing teeth of link plates located at widthwise opposite ends projectoutwardly with respect to the chain and the meshing teeth of theremaining link plates project inwardly with respect to the chain; and asprocket for meshing with a double-meshing-type silent chain, saidsprocket including a meshing element having teeth formed on an outercircumference thereof for meshing engagement with said meshing teeth ofthe link plates which are oriented inwardly with respect to the chain,two buffer-ring support elements each having a cylindrical outer surfaceand provided concentrically on opposite sides of said meshing element,and two buffer rings each having an inside diameter larger than theoutside diameter of said buffer-ring support elements and each beingfloatingly fitted around said cylindrical outer surface of one of saidbuffer-ring support elements while said buffer rings are prevented frommoving in the axial direction relative to the corresponding buffer-ringsupport elements, wherein said buffer rings each have an outerperipheral surface adapted to be in abutment with said flat back facesof the link plates at positions in front and in rear of a meshingposition at which the meshing teeth of the link plates are in mesh withsaid meshing teeth of said meshing element, and at said meshingposition, said outer peripheral surface of each of said buffer rings isseparated from said flat back faces of the link plates and an innerperipheral surface of each of said buffer rings is in abutment with saidcylindrical outer surface of one of said buffer-ring support elements.12. A double-meshing-type silent chain drive according to claim 11,wherein, in each link, the meshing teeth of some link plates oriented inone direction project beyond the back faces of the remaining link platesoriented in an opposite direction.
 13. A double-meshing-type silentchain drive according to claim 11, wherein said buffer ring is formedfrom a metallic material.
 14. A double-meshing-type silent chain driveaccording to claim 11, wherein said buffer ring is formed from anonmetallic material, said non-metallic material including rubber and aresin material.
 15. A double-meshing-type silent chain drive accordingto claim 11, further including two anti-displacement flanges attached toopposite end faces of said buffer-ring support elements so as to preventeach of said buffer rings from displacing in the axial direction betweenone of said flanges and said meshing element.
 16. A sprocket for meshingwith a double-meshing-type silent chain, comprising: a meshing elementhaving meshing teeth formed on an outer circumference thereof formeshing engagement with meshing teeth of link plates which are orientedinwardly with respect to the chain; and two plate-back-face supportelements provided concentrically on opposite sides of said meshingelement and each having a cylindrical outer surface for abutment withflat back faces of link plates of the chain which are oriented inwardlywith respect to the chain.
 17. A sprocket according to claim 16, whereinwhen said cylindrical outer surface of each of said plate-back-facesupport elements is in abutment with the flat back faces of the linkplates, said meshing teeth of said meshing element mesh with the meshingteeth of the opposing link plates at a position offset from a meshingpitch circle of said meshing teeth of said meshing element in a radialoutward direction of said sprocket.
 18. A sprocket according to claim16, wherein said meshing element and said two plate-back-face supportelements are integral with each other.
 19. A sprocket for meshing with adouble-meshing-type silent chain, comprising: a plate-back-face supportelement having a cylindrical outer surface for abutment with flat backfaces of link plates of the chain that are oriented outwardly withrespect to the chain; and two meshing elements provided concentricallyon opposite sides of said plate-end-face support element and each havingmeshing teeth formed on an outer circumference thereof for meshingengagement with meshing teeth of link plates of the chain which areoriented outwardly with respect to the chain, wherein said cylindricalouter surface of said plate-back-face support element is in abutmentwith the flat back faces of the link plates, and said meshing teeth ofeach of said meshing elements mesh with the meshing teeth of theopposing link plates at a position offset from a meshing pitch circle ofsaid meshing teeth of said meshing elements in a radial outwarddirection of said sprocket.
 20. A sprocket for meshing with adouble-meshing-type silent chain, comprising: two meshing elements eachhaving teeth formed on an outer circumference thereof for meshingengagement with meshing teeth of link plates which are orientedoutwardly with respect to the chain; a buffer-ring support elementhaving a cylindrical outer surface and concentrically and integrallyjoining said two meshing elements; and a buffer ring having an insidediameter larger than the outside diameter of said buffer-ring supportelement and being floatingly fitted around said cylindrical outersurface of said buffer-ring support element while said buffer ring isprevented from moving in the axial direction between said two meshingelements, wherein said buffer ring has an outer peripheral surfaceadapted to be in abutment with opposing flat back faces of link platesat positions in front and in rear of a meshing position at which themeshing teeth of the link plates are in mesh with said meshing teeth ofsaid meshing elements, and at said meshing position, said outerperipheral surface of said buffer ring is separated from the flat backfaces of the link plates and an inner peripheral surface of said bufferring is in abutment with said cylindrical outer surface of saidbuffer-ring support element.
 21. A sprocket according to claim 20,wherein said buffer ring is formed from a metallic material.
 22. Asprocket according to claim 20, wherein said buffer ring is formed froma non-metallic material, said nonmetallic material including rubber anda resin material.
 23. A sprocket for meshing with a double-meshing-typesilent chain, comprising: a meshing element having teeth formed on anouter circumference thereof for meshing engagement with meshing teeth oflink plates which are oriented inwardly with respect to the chain; twobuffer-ring support elements each having a cylindrical outer surface andprovided concentrically on opposite sides of said meshing element; andtwo buffer rings each having an inside diameter larger than the outsidediameter of said buffer-ring support elements and each being floatinglyfitted around said cylindrical outer surface of one of said buffer-ringsupport elements while said buffer rings are prevented from moving inthe axial direction relative to the corresponding buffer-ring supportelements, wherein said buffer rings each have an outer peripheralsurface adapted to be in abutment with opposing flat back faces of linkplates at positions in front and in rear of a meshing position at whichthe meshing teeth of the link plates are in mesh with said meshing teethof said meshing element, and at said meshing position, said outerperipheral surface of each of said buffer rings is separated from theflat back faces of the link plates and an inner peripheral surface ofeach of said buffer rings is in abutment with said cylindrical outersurface of one of said buffer-ring support elements.
 24. A sprocketaccording to claim 23, wherein said buffer ring is formed from ametallic material.
 25. A sprocket according to claim 23, wherein saidbuffer ring is formed from a non-metallic material, said nonmetallicmaterial including rubber and a resin material.
 26. A sprocket accordingto claim 23, further including two anti-displacement flanges attached toopposite end faces of said buffer-ring support elements so as to preventeach of said buffer rings from displacing in the axial direction betweenone of said flanges and said meshing element.